The present invention relates to electromagnetic transducers or heads, and particularly to transducers that employ a magnetoresistive mechanism for sensing signals.
The employment of magnetoresistive (MR) elements as sensors for electromagnetic transducers has led to improved performance of heads used in disk and tape drives. As is well known, the resistance of an MR element varies according to the magnetic field impinging upon the element, so that flowing an electric current through the element can be used to determine that magnetic field by measuring the change in resistance.
While bulk materials may exhibit some MR effect, such effects generally become more pronounced as an element becomes smaller relative to the applied electrical and magnetic flux. Thus it is known that films formed of materials such as Permalloy, which is an alloy of nickel and iron having a high permeability and low coercive force, can be useful as sensors for heads when the film thickness is less than about 500 xc3x85. Even thinner films exhibit quantum mechanical effects which are be utilized in types of MR sensors such as spin valve (SV) or giant magnetoresistive (GMR) sensors. Higher storage density associated with smaller recorded bit size also usually requires smaller MR elements.
Generally speaking, the thinner the film used for MR sensing, the more important that the film have a uniform thickness and structure. As such, the material surface or template upon which the film is formed is important. Heads for hard disk drives typically position an MR sensor between a pair of magnetic shields, with the sensor separated from the shields by electrically insulative and nonmagnetic read gaps. The conventional material forming read gaps is aluminum oxide (Al2O3), which is known to be easy to form and work with, and which provides a suitable template for forming thin MR films. Al2O3, however, has a strong affinity for moisture and tends to be porous, both of which can undermine the quality and integrity of an adjoining MR sensor.
U.S. Pat. No. 5,644,455 to Schultz describes forming an MR head read gap of xe2x80x9cdiamond-like carbonxe2x80x9d or xe2x80x9cDLCxe2x80x9d, which is an hydrogenated carbon formed from a gas such as methane (CH4), the DLC having a hydrogen content of 30 to 50 percent. DLC is known to be a hard, thermally conductive, electrically insulative material. DLC also has a high stress, however, making formation of a delicate MR sensor atop a DLC gap difficult.
In an article entitled Ultra-Thin Overcoats For The Head/Disk Interface Tribology, Bhatia et al. propose the use of cathodic arc deposition of carbon to form a coating for a slider or disk. This technique had formerly been used for forming a hard coating on metal tools, and involves melting and vaporizing a carbon cathode with a plasma arc, and directing the carbon ions and particles ejected from the cathode toward a target. Although filters can remove most particles, the resulting films may be rough and have much higher stress than DLC, making even adhesion to a substrate problematic.
The present invention involves forming thin layers of tetrahedral amorphous carbon (t-aC) for MR sensors. The layers of t-aC have essentially zero concentration of hydrogen and can serve as read gaps for the sensors. Such a hydrogen-free t-aC read gap has an improved thermal conductivity that helps to keep an adjoining MR sensor from overheating during operation. This improved thermal conductivity of the read gap can extend sensor lifetimes and/or improve sensor performance. Hydrogen-free t-aC has a thermal conductivity that may be more than double that of conventional DLC and more than ten times that of Al2O3.
Moreover, the hydrogen-free t-aC read gap of the present invention has reduced defects and porosity, which prevents unwanted electrical conduction or shorting between a sensor and a shield. Hydrogen-free t-aC also is much harder than DLC, which in turn is known to be many times harder than Al2O3. This extreme hardness renders the read gap layers of the present invention impervious to plasma and chemical etching processes such as ion milling that are used to form the sensor. The increased hardness and reduced defects and porosity allow the read gaps to be made thinner without risking electrical shorting.
The effects of the inherently high stress of the hydrogen-free t-aC layers can be minimized by keeping the read gap thickness preferably less than a few hundred angstroms, avoiding adhesion problems that such high stress might otherwise cause. While such thin read gaps cannot be made reliably with conventional materials due to shorting and other problems, the hydrogen-free t-aC read gaps of the present invention can form read gaps as thin as twenty angstroms. Such thin read gaps can improve the focus of the sensor and shorten the path to heat sinks provided by the shields, further improving performance.
Thin t-aC layers of the present invention can be beneficially employed for sensor elements beside read gaps. For example, a thin t-aC layer can be used to separate a magnetoresistive layer from an adjacent bias layer for an anisotropic magnetoresistive sensor. In addition, a relatively thin t-aC layer can be disposed between plural sensors of a dual stripe MR head. In these examples as well as others the relatively thin t-aC layers offer performance improvements that include increased resolution and reliability.